1. Field of the Invention
The present invention relates to an indicating apparatus which is used for indicating a state of various types of equipment and for alarm-indicating an abnormal operating state of various types of equipment by applying light through a synthetic resin base plate, and for illuminating an indicating plate produced of synthetic resin.
2. Description of the Prior Art
Indicating apparatus adapted to apply light from a light source to a light-transmitting synthetic resin base plate to cause the base plate to glitter, have been known in the prior art as have been disclosed in, for example, U.S. Pat. No. 3,017,609 and U.S. Pat. No. 4,447,860.
Using an indicating apparatus to be mounted on motor vehicles as an example, this type of conventional indicating apparatus will be explained. An instrument housing is mounted in an instrument panel on a vehicle. Within this housing, indicating apparatus are mounted to indicate to a driver the location of a trouble occurring in each part of the vehicle or the operating condition of various equipment. Generally, the instrument built in the above-described housing has, in a part of its dial plate, a cutout window section having the same number of cutouts as items of vehicle to be indicated. In each of these cutout windows is disposed a base plate produced of such a synthetic resin which has light-transmission properties, e.g. polycarbonate resin, acrylic resin or AS resin. Each of the cells is defined at the back of the above-described dial plate by a partition wall surrounding each synthetic resin base plate. At the bottom of each of these cells is installed a light source. When this light source is turned on to apply a transmitting light of illumination to the synthetic resin base plate (which is an indicating plate) the plate glitters, indicating the operating state of each part of vehicle and the location of any detected trouble. In this case, with its visibility taken into consideration, the aforementioned synthetic resin base plate for the indicating plate known in prior art as suggested for example in Laid-Open Japanese Utility Model No. Sho 52-150340 published by the Patent Office of Japan, is processed into a diamond-cut form on the back side, whereby the plate glitters by refraction, reflection, diffusion and concentration of light from the light source, insuring easy reading of the indicating plate from the front.
However, there is a problem in that, for the manufacture of the diamond-cut portion comprising the concave and convex section formed on the aforesaid indicating plate, an indicating plate molding die of complicated configuration is required, which, therefore, takes time, resulting in a high die cost.
Considering the above-described problem, I have proposed a solution wherein a first colored layer is formed by printing on one side of a transparent synthetic resin base plate, and on this first colored layer is further formed a second colored layer provided with a number of for example round punched holes. (Refer to Laid-Open Japanese Utility Model No. Sho 58-149774 published by the Patent Office of Japan.)
The indicating plate of this indicating apparatus is of such a design that when the light from the light source is applied to the base plate, the portion excluding the above-described punched holes is illuminated through the first and second colored layers that have been laminated, while the punched hole portion is illuminated through the first colored layer alone, and accordingly the transmission factor by the light applied from the light source is high in the punched hole portion and low in regions other than the punched hole portion. In consequence, when viewed from the front of the base plate, the punched hole portion glitters and the other portion is faintly illuminated, thus providing an effect of illumination as if the base plate itself were cut into a lens-like form.
However, for the indicating plate of the indicating apparatus that has been constituted as such, it will sometimes become difficult to obtain a deep illumination effect because the brightness and dimness of light depends only upon a difference in the amount of light passing through each colored layer provided only upon the base plate 1.